In facilities having extremely harsh working conditions, such as in the extractive industries (mainly the mining industry), as well as in the construction industry, the frequent mechanical abuse to elements conducting electrical and/or telecommunications signals found in low or null lighting areas is well known. The above makes the elements having a cover without a fast and easy visualization effect, since they cannot be seen, to be exposed to hits, crushings, or other damages due to the severe operation conditions where they are placed.
To solve the issues in extremely harsh environments such as mines, there are cable covers classified by the applicable product standards such as heavy-duty (HD) and extra heavy-duty use (XHD). In facilities such as mines, based on the cable gauge as an end-product, and the destined environment, the external cover can be manufactured with abrasion resistant materials such as CPE (chlorinated polyethylene), CR (Polychloroprene), CSM (chloro-sulphonated Polyethylene), NBR-PVC (Acrylonitrile butadiene-styrene/Polyvinyl chloride) and TPU (thermoplastic Polyurethane).
Likewise, there are other application fields with less resistance requirements for energy and/or telecommunications cable covers with respect to resistance due to mechanical abuse. For these applications, materials used defined by the different product standards include, but are not limited to, materials such as PE (polyethylene), PA (polyamides), PP (polypropylene), PVC (Polyvinyl chloride) and Polyester as the mainly used polymeric compounds.
In the prior art, there are several alternatives of materials for energy and/or telecommunications cable covers, which try to solve the low or null visibility of the cover of these cables once installed in harsh and low or null lighting environments.
In Patent Application WO 00/30126, an option for a mechanical reinforcement for cables is disclosed, consisting of external application of a urethane-based material on the above-mentioned extra heavy-duty cover materials. Applying a urethane-based coating offers a higher abrasion resistance; furthermore, this coating is transparent, such that it allows seeing the cover color of the cable desired to be protected; however, this solution does not consider the use of luminescent materials to give the cable better visibility.
On the other hand, in Patent Application WO 82/03942 a way to solve the visibility of energy transmitting cables used in the mining industry is disclosed, which consists in the application of a continuous reflective tape applied on the cable cover before this is subjected to a vulcanization process, then the reflective tape remains embedded in the external part of the cover by a process including encapsulating the whole cable under a melted lead covering, thereby the cover is vulcanized and the lead is subsequently withdrawn thus leaving the reflective strip embedded in the already vulcanized rubber covering (reticulated).
Similarly, in U.S. Patent Application 20100282491 the application of an extruded cover of fluorescent material on the conductor bundle (core) of the cable pretended to be protected is described, and on this first layer, a second layer made of a light-transmitting thermoplastic polyurethane (TPU) surrounding the first layer is deposited. This solution is not as good when the TPU material must be flame resistant, since the additives employed to give this resistance cause the second layer to have an opaque natural color, limiting the brightness effect of the inner layer. An embodiment described in this very patent application consists in the application of a layer arranged between the first layer and the external layer of TPU material, such that the application of the intermediate layer may be a reinforcing mesh with empty spaces such that it allows visualizing the first layer. In both embodiments in this patent, the first layer may be a tape having a fluorescent external covering wrapping the conductor bundle remaining under the cover.
In Patent Application WO 2010 131084, an external cover of a fluorescent pigments material is described, being mentioned that this cover has a drawback related to low durability of the fluorescent pigments, due to exposure to the working environment, i.e., to the air, water, soil and ultraviolet light (UV rays) conditions the external cover is exposed to. In the same document, as a solution to the above problem the use of a reflective tape arranged helically on the cable external cover is suggested. The defect of this solution is that the reflective tape is easily destroyed as a result of severe handling or abrasive environments. Another embodiment set forth is the application of fluorescent tapes, reflective tapes or a combination thereof, helically arranged on the conductor or the conductor bundle, wherein the tapes are protected by deposition of a light-transmitting thermoplastic Polyurethane (TPU) layer surrounding the first layer. This solution is limited when the TPU material must be flame resistant, since the additives used to give this resistance turn the second layer to an opaque natural color, considerably limiting the brightness effect of the inner layer. It also has the drawback that the light-transmitting TPU material turns opaque by the aging effect of the material.
In the same document WO 2010 131084, it is set forth that a first layer consisting of a luminescent tape or polymeric reflective material is deposited on the conductor or conductor bundle, and onto the latter, add a second layer consisting of transparent polyesther tapes, which protect the luminescent or reflective tapes during the application of the last cover layer consisting of a light-transmitting thermoplastic polyurethane (TPU). Whereby in this solution there is no adherence between the first and third layers, then, it cannot be considered as an integral cover. Additionally, any departure from the application process of this configuration may cause loss of the polyester layer coating, resulting in the TPU material being in contact with the first layer; and, therefore, its capability of luminescence or reflectance may be exhausted.
On the other hand, in the Utility Model Registration Application CN201886811U a conductor or conductor bundle is described onto which a layer of material meeting the mechanical, chemical and electrical requirements as a cover for an electric cable product is applied. Over this layer, a helical reflective tape with covering spaces from 30% to 60% is applied, which is protected by a thin TPU layer having thicknesses from 0.5 mm to 1.2 mm, and which function is to protect the reflective tape. This solution to the visibility of electric cables in dark environments has the drawback that the reflective tape used is applied as an add-on to the finished cable, then, it results in a cable to which a reflective tape which needs to be protected by a layer of a TPU material is applied with a non-exceeding thickness of 1.2 mm to allow visibility of the reflective tape. The TPU adhesion means on the applied reflective tape do not constitute an integral cover with reflective elements forming part of the same cover, rather being add-on elements installed on the cover.
In U.S. Patent Application 20020012795A1 a wiring to which a helical or longitudinal tape of opaque enough material is applied is disclosed, with at least one light reflective effect face, such that it covers 100% of the core it is applied on. A transparent compound is applied on this reflective tape by means of extrusion, typically from PVC, or a pigment may be used on this external layer, which should be translucent to allow seeing the reflective layer coaxially arranged on the core. This solution has limited applications, since direct lightings are required for the light to reflect, also, the mechanical properties of the PVC cover are not proper to be used in harsh environments. It is worth mentioning that this document does not cover applications in electric or telecommunications cables.
Finally, in U.S. Pat. No. 6,660,378B2 a light duty wiring is described, such as that used for animal leashes, pedestrian crossing signals, restraining walls, etc., to which an inner layer wrapping the wiring is applied, and above this layer, a layer having a sensitively lower thickness than the first layer (coating) is applied, which is formed of a resilient polymer with a dark glowing material, which is pulverized for its dispersion in the coating layer. The inner layer has a luminous color, or a reflective surface such that the largest portion of light incident on this cable is reflected, having the great defect that this solution is for a low harsh environment use. As the above document, this document does not cover applications in electric or telecommunications cables.
As it may be seen, in the state of the art the use of reflective materials to coat electric cables conducting electric and/or telecommunications signals is disclosed; however, the reflective materials described in the prior art have the defect of not solving the poor or null visibility of these cables covers in a proper manner once installed in harsh environments and with low or null lighting, added to the fact that they do not form an integral protection cover.
Due to the above, it has been sought to suppress the objections found in the state of the art by means of the development of electric and/or telecommunications cables having retro-reflective integral covers for use in harsh environments with low or null visibility, and the manufacturing process thereof.